• Dmitry Kasatkin's avatar
    ima: re-introduce own integrity cache lock · 0d73a552
    Dmitry Kasatkin authored
    Before IMA appraisal was introduced, IMA was using own integrity cache
    lock along with i_mutex. process_measurement and ima_file_free took
    the iint->mutex first and then the i_mutex, while setxattr, chmod and
    chown took the locks in reverse order. To resolve the potential deadlock,
    i_mutex was moved to protect entire IMA functionality and the redundant
    iint->mutex was eliminated.
    
    Solution was based on the assumption that filesystem code does not take
    i_mutex further. But when file is opened with O_DIRECT flag, direct-io
    implementation takes i_mutex and produces deadlock. Furthermore, certain
    other filesystem operations, such as llseek, also take i_mutex.
    
    More recently some filesystems have replaced their filesystem specific
    lock with the global i_rwsem to read a file.  As a result, when IMA
    attempts to calculate the file hash, reading the file attempts to take
    the i_rwsem again.
    
    To resolve O_DIRECT related deadlock problem, this patch re-introduces
    iint->mutex. But to eliminate the original chmod() related deadlock
    problem, this patch eliminates the requirement for chmod hooks to take
    the iint->mutex by introducing additional atomic iint->attr_flags to
    indicate calling of the hooks. The allowed locking order is to take
    the iint->mutex first and then the i_rwsem.
    
    Original flags were cleared in chmod(), setxattr() or removwxattr()
    hooks and tested when file was closed or opened again. New atomic flags
    are set or cleared in those hooks and tested to clear iint->flags on
    close or on open.
    
    Atomic flags are following:
    * IMA_CHANGE_ATTR - indicates that chATTR() was called (chmod, chown,
      chgrp) and file attributes have changed. On file open, it causes IMA
      to clear iint->flags to re-evaluate policy and perform IMA functions
      again.
    * IMA_CHANGE_XATTR - indicates that setxattr or removexattr was called
      and extended attributes have changed. On file open, it causes IMA to
      clear iint->flags IMA_DONE_MASK to re-appraise.
    * IMA_UPDATE_XATTR - indicates that security.ima needs to be updated.
      It is cleared if file policy changes and no update is needed.
    * IMA_DIGSIG - indicates that file security.ima has signature and file
      security.ima must not update to file has on file close.
    * IMA_MUST_MEASURE - indicates the file is in the measurement policy.
    
    Fixes: Commit 65523218 ("xfs: remove i_iolock and use i_rwsem in
    the VFS inode instead")
    Signed-off-by: default avatarDmitry Kasatkin <dmitry.kasatkin@huawei.com>
    Signed-off-by: default avatarMimi Zohar <zohar@linux.vnet.ibm.com>
    0d73a552
integrity.h 5.25 KB